Hi everyone, been awhile since i have been here. So my problem is when i am sitting idling at a red light or in a parking lot, my RPMs run steady at 500, then all of a sudden rpms will drop to about a 100 like it is going to stall then it jumps right back up. Any suggestions would be appreciated.....98 LST, 4.3L, 4WD....fuel pump was replaced 4 years ago

 

I had the same problem, and in my case it was the brake booster.

If the brake pedal is sinking to the floor as idle drops, then the brake booster or brake booster valve could be faulty.

 

Thanks, i never noticed if it does will pay more attention to it,

 

First guess, ignition module. They cut out at idle/ low speeds a few times then leave you stranded in an intersection!

Connect a timing light to the coil wire, tape the light to the hood so you can see the flashing while driving. The light will become erratic if the ignition cuts out.

 

Thanks, going to switch this out and hope it works, it is probably 27 years old, dont have access to a timing light

 

After looking at this dont look like a big project, probably going to change coil pack too...Thanks

 

okay so changing these didnt help. My next question is there a easier way to change the IAC valve without having to take the throttle body apart